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Date: Tue, 13 Jun 2023 09:21:32 -0400
From: Phil Auld <pauld@...hat.com>
To: Daniel Bristot de Oliveira <bristot@...nel.org>
Cc: Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Valentin Schneider <vschneid@...hat.com>,
linux-kernel@...r.kernel.org,
Luca Abeni <luca.abeni@...tannapisa.it>,
Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>,
Thomas Gleixner <tglx@...utronix.de>,
Joel Fernandes <joel@...lfernandes.org>,
Vineeth Pillai <vineeth@...byteword.org>,
Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [RFC PATCH V3 4/6] sched/deadline: Introduce deadline servers
Hi,
On Thu, Jun 08, 2023 at 05:58:16PM +0200 Daniel Bristot de Oliveira wrote:
> From: Peter Zijlstra <peterz@...radead.org>
>
> Low priority tasks (e.g., SCHED_OTHER) can suffer starvation if tasks
> with higher priority (e.g., SCHED_FIFO) monopolize CPU(s).
>
> RT Throttling has been introduced a while ago as a (mostly debug)
> countermeasure one can utilize to reserve some CPU time for low priority
> tasks (usually background type of work, e.g. workqueues, timers, etc.).
> It however has its own problems (see documentation) and the undesired
> effect of unconditionally throttling FIFO tasks even when no lower
> priority activity needs to run (there are mechanisms to fix this issue
> as well, but, again, with their own problems).
>
> Introduce deadline servers to service low priority tasks needs under
> starvation conditions. Deadline servers are built extending SCHED_DEADLINE
> implementation to allow 2-level scheduling (a sched_deadline entity
> becomes a container for lower priority scheduling entities).
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Signed-off-by: Daniel Bristot de Oliveira <bristot@...nel.org>
> ---
> include/linux/sched.h | 22 ++-
> kernel/sched/core.c | 17 ++
> kernel/sched/deadline.c | 350 +++++++++++++++++++++++++++-------------
> kernel/sched/fair.c | 4 +
> kernel/sched/sched.h | 29 ++++
> 5 files changed, 309 insertions(+), 113 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 26b1925a702a..4c90d7693a75 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -64,12 +64,14 @@ struct robust_list_head;
> struct root_domain;
> struct rq;
> struct sched_attr;
> +struct sched_dl_entity;
> struct sched_param;
> struct seq_file;
> struct sighand_struct;
> struct signal_struct;
> struct task_delay_info;
> struct task_group;
> +struct task_struct;
> struct user_event_mm;
>
> /*
> @@ -600,6 +602,9 @@ struct sched_rt_entity {
> #endif
> } __randomize_layout;
>
> +typedef bool (*dl_server_has_tasks_f)(struct sched_dl_entity *);
> +typedef struct task_struct *(*dl_server_pick_f)(struct sched_dl_entity *);
> +
> struct sched_dl_entity {
> struct rb_node rb_node;
>
> @@ -647,6 +652,7 @@ struct sched_dl_entity {
> unsigned int dl_yielded : 1;
> unsigned int dl_non_contending : 1;
> unsigned int dl_overrun : 1;
> + unsigned int dl_server : 1;
>
> /*
> * Bandwidth enforcement timer. Each -deadline task has its
> @@ -661,7 +667,20 @@ struct sched_dl_entity {
> * timer is needed to decrease the active utilization at the correct
> * time.
> */
> - struct hrtimer inactive_timer;
> + struct hrtimer inactive_timer;
> +
> + /*
> + * Bits for DL-server functionality. Also see the comment near
> + * dl_server_update().
> + *
> + * @rq the runqueue this server is for
> + *
> + * @server_has_tasks() returns true if @server_pick return a
> + * runnable task.
> + */
> + struct rq *rq;
> + dl_server_has_tasks_f server_has_tasks;
> + dl_server_pick_f server_pick;
>
> #ifdef CONFIG_RT_MUTEXES
> /*
> @@ -790,6 +809,7 @@ struct task_struct {
> struct sched_entity se;
> struct sched_rt_entity rt;
> struct sched_dl_entity dl;
> + struct sched_dl_entity *server;
> const struct sched_class *sched_class;
I like the cleanups in the first 3 patches a lot. I'm still wrapping my head
around the rest. But "server" is a very non-descript, generic term for
something in task_struct. Maybe "sched_server" or something?
Cheers,
Phil
>
> #ifdef CONFIG_SCHED_CORE
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index e34b02cbe41f..5b88b822ec89 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3803,6 +3803,8 @@ ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags,
> rq->idle_stamp = 0;
> }
> #endif
> +
> + p->server = NULL;
> }
>
> /*
> @@ -6013,12 +6015,27 @@ __pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
> p = pick_next_task_idle(rq);
> }
>
> + /*
> + * This is the fast path; it cannot be a DL server pick;
> + * therefore even if @p == @prev, ->server must be NULL.
> + */
> + if (p->server)
> + p->server = NULL;
> +
> return p;
> }
>
> restart:
> put_prev_task_balance(rq, prev, rf);
>
> + /*
> + * We've updated @prev and no longer need the server link, clear it.
> + * Must be done before ->pick_next_task() because that can (re)set
> + * ->server.
> + */
> + if (prev->server)
> + prev->server = NULL;
> +
> for_each_class(class) {
> p = class->pick_next_task(rq);
> if (p)
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 869734eecb2c..c67056ff5749 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -52,8 +52,14 @@ static int __init sched_dl_sysctl_init(void)
> late_initcall(sched_dl_sysctl_init);
> #endif
>
> +static bool dl_server(struct sched_dl_entity *dl_se)
> +{
> + return dl_se->dl_server;
> +}
> +
> static inline struct task_struct *dl_task_of(struct sched_dl_entity *dl_se)
> {
> + BUG_ON(dl_server(dl_se));
> return container_of(dl_se, struct task_struct, dl);
> }
>
> @@ -62,14 +68,22 @@ static inline struct rq *rq_of_dl_rq(struct dl_rq *dl_rq)
> return container_of(dl_rq, struct rq, dl);
> }
>
> -static inline struct dl_rq *dl_rq_of_se(struct sched_dl_entity *dl_se)
> +static inline struct rq *rq_of_dl_se(struct sched_dl_entity *dl_se)
> {
> - struct task_struct *p = dl_task_of(dl_se);
> - struct rq *rq = task_rq(p);
> + struct rq *rq = dl_se->rq;
> +
> + if (!dl_server(dl_se))
> + rq = task_rq(dl_task_of(dl_se));
>
> - return &rq->dl;
> + return rq;
> }
>
> +static inline struct dl_rq *dl_rq_of_se(struct sched_dl_entity *dl_se)
> +{
> + return &rq_of_dl_se(dl_se)->dl;
> +}
> +
> +
> static inline int on_dl_rq(struct sched_dl_entity *dl_se)
> {
> return !RB_EMPTY_NODE(&dl_se->rb_node);
> @@ -392,9 +406,8 @@ static void __dl_clear_params(struct sched_dl_entity *dl_se);
> static void task_non_contending(struct sched_dl_entity *dl_se)
> {
> struct hrtimer *timer = &dl_se->inactive_timer;
> - struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
> - struct rq *rq = rq_of_dl_rq(dl_rq);
> - struct task_struct *p = dl_task_of(dl_se);
> + struct rq *rq = rq_of_dl_se(dl_se);
> + struct dl_rq *dl_rq = &rq->dl;
> s64 zerolag_time;
>
> /*
> @@ -424,25 +437,33 @@ static void task_non_contending(struct sched_dl_entity *dl_se)
> * utilization now, instead of starting a timer
> */
> if ((zerolag_time < 0) || hrtimer_active(&dl_se->inactive_timer)) {
> - if (dl_task(p))
> + if (dl_server(dl_se)) {
> sub_running_bw(dl_se, dl_rq);
> + } else {
> + struct task_struct *p = dl_task_of(dl_se);
> +
> + if (dl_task(p))
> + sub_running_bw(dl_se, dl_rq);
>
> - if (!dl_task(p) || READ_ONCE(p->__state) == TASK_DEAD) {
> - struct dl_bw *dl_b = dl_bw_of(task_cpu(p));
> + if (!dl_task(p) || READ_ONCE(p->__state) == TASK_DEAD) {
> + struct dl_bw *dl_b = dl_bw_of(task_cpu(p));
>
> - if (READ_ONCE(p->__state) == TASK_DEAD)
> - sub_rq_bw(dl_se, &rq->dl);
> - raw_spin_lock(&dl_b->lock);
> - __dl_sub(dl_b, dl_se->dl_bw, dl_bw_cpus(task_cpu(p)));
> - raw_spin_unlock(&dl_b->lock);
> - __dl_clear_params(dl_se);
> + if (READ_ONCE(p->__state) == TASK_DEAD)
> + sub_rq_bw(dl_se, &rq->dl);
> + raw_spin_lock(&dl_b->lock);
> + __dl_sub(dl_b, dl_se->dl_bw, dl_bw_cpus(task_cpu(p)));
> + raw_spin_unlock(&dl_b->lock);
> + __dl_clear_params(dl_se);
> + }
> }
>
> return;
> }
>
> dl_se->dl_non_contending = 1;
> - get_task_struct(p);
> + if (!dl_server(dl_se))
> + get_task_struct(dl_task_of(dl_se));
> +
> hrtimer_start(timer, ns_to_ktime(zerolag_time), HRTIMER_MODE_REL_HARD);
> }
>
> @@ -469,8 +490,10 @@ static void task_contending(struct sched_dl_entity *dl_se, int flags)
> * will not touch the rq's active utilization,
> * so we are still safe.
> */
> - if (hrtimer_try_to_cancel(&dl_se->inactive_timer) == 1)
> - put_task_struct(dl_task_of(dl_se));
> + if (hrtimer_try_to_cancel(&dl_se->inactive_timer) == 1) {
> + if (!dl_server(dl_se))
> + put_task_struct(dl_task_of(dl_se));
> + }
> } else {
> /*
> * Since "dl_non_contending" is not set, the
> @@ -483,10 +506,8 @@ static void task_contending(struct sched_dl_entity *dl_se, int flags)
> }
> }
>
> -static inline int is_leftmost(struct task_struct *p, struct dl_rq *dl_rq)
> +static inline int is_leftmost(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
> {
> - struct sched_dl_entity *dl_se = &p->dl;
> -
> return rb_first_cached(&dl_rq->root) == &dl_se->rb_node;
> }
>
> @@ -573,8 +594,6 @@ static void inc_dl_migration(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
>
> if (p->nr_cpus_allowed > 1)
> dl_rq->dl_nr_migratory++;
> -
> - update_dl_migration(dl_rq);
> }
>
> static void dec_dl_migration(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
> @@ -583,8 +602,6 @@ static void dec_dl_migration(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
>
> if (p->nr_cpus_allowed > 1)
> dl_rq->dl_nr_migratory--;
> -
> - update_dl_migration(dl_rq);
> }
>
> #define __node_2_pdl(node) \
> @@ -762,8 +779,10 @@ static inline void deadline_queue_pull_task(struct rq *rq)
> }
> #endif /* CONFIG_SMP */
>
> +static void
> +enqueue_dl_entity(struct sched_dl_entity *dl_se, int flags);
> static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags);
> -static void __dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags);
> +static void dequeue_dl_entity(struct sched_dl_entity *dl_se, int flags);
> static void check_preempt_curr_dl(struct rq *rq, struct task_struct *p, int flags);
>
> static inline void replenish_dl_new_period(struct sched_dl_entity *dl_se,
> @@ -1011,8 +1030,7 @@ static inline bool dl_is_implicit(struct sched_dl_entity *dl_se)
> */
> static void update_dl_entity(struct sched_dl_entity *dl_se)
> {
> - struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
> - struct rq *rq = rq_of_dl_rq(dl_rq);
> + struct rq *rq = rq_of_dl_se(dl_se);
>
> if (dl_time_before(dl_se->deadline, rq_clock(rq)) ||
> dl_entity_overflow(dl_se, rq_clock(rq))) {
> @@ -1043,11 +1061,11 @@ static inline u64 dl_next_period(struct sched_dl_entity *dl_se)
> * actually started or not (i.e., the replenishment instant is in
> * the future or in the past).
> */
> -static int start_dl_timer(struct task_struct *p)
> +static int start_dl_timer(struct sched_dl_entity *dl_se)
> {
> - struct sched_dl_entity *dl_se = &p->dl;
> struct hrtimer *timer = &dl_se->dl_timer;
> - struct rq *rq = task_rq(p);
> + struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
> + struct rq *rq = rq_of_dl_rq(dl_rq);
> ktime_t now, act;
> s64 delta;
>
> @@ -1081,13 +1099,33 @@ static int start_dl_timer(struct task_struct *p)
> * and observe our state.
> */
> if (!hrtimer_is_queued(timer)) {
> - get_task_struct(p);
> + if (!dl_server(dl_se))
> + get_task_struct(dl_task_of(dl_se));
> hrtimer_start(timer, act, HRTIMER_MODE_ABS_HARD);
> }
>
> return 1;
> }
>
> +static void __push_dl_task(struct rq *rq, struct rq_flags *rf)
> +{
> +#ifdef CONFIG_SMP
> + /*
> + * Queueing this task back might have overloaded rq, check if we need
> + * to kick someone away.
> + */
> + if (has_pushable_dl_tasks(rq)) {
> + /*
> + * Nothing relies on rq->lock after this, so its safe to drop
> + * rq->lock.
> + */
> + rq_unpin_lock(rq, rf);
> + push_dl_task(rq);
> + rq_repin_lock(rq, rf);
> + }
> +#endif
> +}
> +
> /*
> * This is the bandwidth enforcement timer callback. If here, we know
> * a task is not on its dl_rq, since the fact that the timer was running
> @@ -1106,10 +1144,34 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
> struct sched_dl_entity *dl_se = container_of(timer,
> struct sched_dl_entity,
> dl_timer);
> - struct task_struct *p = dl_task_of(dl_se);
> + struct task_struct *p;
> struct rq_flags rf;
> struct rq *rq;
>
> + if (dl_server(dl_se)) {
> + struct rq *rq = rq_of_dl_se(dl_se);
> + struct rq_flags rf;
> +
> + rq_lock(rq, &rf);
> + if (dl_se->dl_throttled) {
> + sched_clock_tick();
> + update_rq_clock(rq);
> +
> + if (dl_se->server_has_tasks(dl_se)) {
> + enqueue_dl_entity(dl_se, ENQUEUE_REPLENISH);
> + resched_curr(rq);
> + __push_dl_task(rq, &rf);
> + } else {
> + replenish_dl_entity(dl_se);
> + }
> +
> + }
> + rq_unlock(rq, &rf);
> +
> + return HRTIMER_NORESTART;
> + }
> +
> + p = dl_task_of(dl_se);
> rq = task_rq_lock(p, &rf);
>
> /*
> @@ -1180,21 +1242,7 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
> else
> resched_curr(rq);
>
> -#ifdef CONFIG_SMP
> - /*
> - * Queueing this task back might have overloaded rq, check if we need
> - * to kick someone away.
> - */
> - if (has_pushable_dl_tasks(rq)) {
> - /*
> - * Nothing relies on rq->lock after this, so its safe to drop
> - * rq->lock.
> - */
> - rq_unpin_lock(rq, &rf);
> - push_dl_task(rq);
> - rq_repin_lock(rq, &rf);
> - }
> -#endif
> + __push_dl_task(rq, &rf);
>
> unlock:
> task_rq_unlock(rq, p, &rf);
> @@ -1236,12 +1284,11 @@ static void init_dl_task_timer(struct sched_dl_entity *dl_se)
> */
> static inline void dl_check_constrained_dl(struct sched_dl_entity *dl_se)
> {
> - struct task_struct *p = dl_task_of(dl_se);
> - struct rq *rq = rq_of_dl_rq(dl_rq_of_se(dl_se));
> + struct rq *rq = rq_of_dl_se(dl_se);
>
> if (dl_time_before(dl_se->deadline, rq_clock(rq)) &&
> dl_time_before(rq_clock(rq), dl_next_period(dl_se))) {
> - if (unlikely(is_dl_boosted(dl_se) || !start_dl_timer(p)))
> + if (unlikely(is_dl_boosted(dl_se) || !start_dl_timer(dl_se)))
> return;
> dl_se->dl_throttled = 1;
> if (dl_se->runtime > 0)
> @@ -1296,29 +1343,13 @@ static u64 grub_reclaim(u64 delta, struct rq *rq, struct sched_dl_entity *dl_se)
> return (delta * u_act) >> BW_SHIFT;
> }
>
> -/*
> - * Update the current task's runtime statistics (provided it is still
> - * a -deadline task and has not been removed from the dl_rq).
> - */
> -static void update_curr_dl(struct rq *rq)
> +static inline void
> +update_stats_dequeue_dl(struct dl_rq *dl_rq, struct sched_dl_entity *dl_se,
> + int flags);
> +static void update_curr_dl_se(struct rq *rq, struct sched_dl_entity *dl_se, s64 delta_exec)
> {
> - struct task_struct *curr = rq->curr;
> - struct sched_dl_entity *dl_se = &curr->dl;
> - s64 delta_exec, scaled_delta_exec;
> - int cpu = cpu_of(rq);
> -
> - if (!dl_task(curr) || !on_dl_rq(dl_se))
> - return;
> + s64 scaled_delta_exec;
>
> - /*
> - * Consumed budget is computed considering the time as
> - * observed by schedulable tasks (excluding time spent
> - * in hardirq context, etc.). Deadlines are instead
> - * computed using hard walltime. This seems to be the more
> - * natural solution, but the full ramifications of this
> - * approach need further study.
> - */
> - delta_exec = update_curr_common(rq);
> if (unlikely(delta_exec <= 0)) {
> if (unlikely(dl_se->dl_yielded))
> goto throttle;
> @@ -1336,10 +1367,9 @@ static void update_curr_dl(struct rq *rq)
> * according to current frequency and CPU maximum capacity.
> */
> if (unlikely(dl_se->flags & SCHED_FLAG_RECLAIM)) {
> - scaled_delta_exec = grub_reclaim(delta_exec,
> - rq,
> - &curr->dl);
> + scaled_delta_exec = grub_reclaim(delta_exec, rq, dl_se);
> } else {
> + int cpu = cpu_of(rq);
> unsigned long scale_freq = arch_scale_freq_capacity(cpu);
> unsigned long scale_cpu = arch_scale_cpu_capacity(cpu);
>
> @@ -1358,11 +1388,21 @@ static void update_curr_dl(struct rq *rq)
> (dl_se->flags & SCHED_FLAG_DL_OVERRUN))
> dl_se->dl_overrun = 1;
>
> - __dequeue_task_dl(rq, curr, 0);
> - if (unlikely(is_dl_boosted(dl_se) || !start_dl_timer(curr)))
> - enqueue_task_dl(rq, curr, ENQUEUE_REPLENISH);
> + dequeue_dl_entity(dl_se, 0);
> + if (!dl_server(dl_se)) {
> + /* XXX: After v2, from __dequeue_task_dl() */
> + update_stats_dequeue_dl(&rq->dl, dl_se, 0);
> + dequeue_pushable_dl_task(rq, dl_task_of(dl_se));
> + }
> +
> + if (unlikely(is_dl_boosted(dl_se) || !start_dl_timer(dl_se))) {
> + if (dl_server(dl_se))
> + enqueue_dl_entity(dl_se, ENQUEUE_REPLENISH);
> + else
> + enqueue_task_dl(rq, dl_task_of(dl_se), ENQUEUE_REPLENISH);
> + }
>
> - if (!is_leftmost(curr, &rq->dl))
> + if (!is_leftmost(dl_se, &rq->dl))
> resched_curr(rq);
> }
>
> @@ -1392,20 +1432,82 @@ static void update_curr_dl(struct rq *rq)
> }
> }
>
> +void dl_server_update(struct sched_dl_entity *dl_se, s64 delta_exec)
> +{
> + update_curr_dl_se(dl_se->rq, dl_se, delta_exec);
> +}
> +
> +void dl_server_start(struct sched_dl_entity *dl_se)
> +{
> + if (!dl_server(dl_se)) {
> + dl_se->dl_server = 1;
> + setup_new_dl_entity(dl_se);
> + }
> + enqueue_dl_entity(dl_se, ENQUEUE_WAKEUP);
> +}
> +
> +void dl_server_stop(struct sched_dl_entity *dl_se)
> +{
> + dequeue_dl_entity(dl_se, DEQUEUE_SLEEP);
> +}
> +
> +void dl_server_init(struct sched_dl_entity *dl_se, struct rq *rq,
> + dl_server_has_tasks_f has_tasks,
> + dl_server_pick_f pick)
> +{
> + dl_se->rq = rq;
> + dl_se->server_has_tasks = has_tasks;
> + dl_se->server_pick = pick;
> +}
> +
> +/*
> + * Update the current task's runtime statistics (provided it is still
> + * a -deadline task and has not been removed from the dl_rq).
> + */
> +static void update_curr_dl(struct rq *rq)
> +{
> + struct task_struct *curr = rq->curr;
> + struct sched_dl_entity *dl_se = &curr->dl;
> + s64 delta_exec;
> +
> + if (!dl_task(curr) || !on_dl_rq(dl_se))
> + return;
> +
> + /*
> + * Consumed budget is computed considering the time as
> + * observed by schedulable tasks (excluding time spent
> + * in hardirq context, etc.). Deadlines are instead
> + * computed using hard walltime. This seems to be the more
> + * natural solution, but the full ramifications of this
> + * approach need further study.
> + */
> + delta_exec = update_curr_common(rq);
> + update_curr_dl_se(rq, dl_se, delta_exec);
> +}
> +
> static enum hrtimer_restart inactive_task_timer(struct hrtimer *timer)
> {
> struct sched_dl_entity *dl_se = container_of(timer,
> struct sched_dl_entity,
> inactive_timer);
> - struct task_struct *p = dl_task_of(dl_se);
> + struct task_struct *p = NULL;
> struct rq_flags rf;
> struct rq *rq;
>
> - rq = task_rq_lock(p, &rf);
> + if (!dl_server(dl_se)) {
> + p = dl_task_of(dl_se);
> + rq = task_rq_lock(p, &rf);
> + } else {
> + rq = dl_se->rq;
> + rq_lock(rq, &rf);
> + }
>
> sched_clock_tick();
> update_rq_clock(rq);
>
> + if (dl_server(dl_se))
> + goto no_task;
> +
> if (!dl_task(p) || READ_ONCE(p->__state) == TASK_DEAD) {
> struct dl_bw *dl_b = dl_bw_of(task_cpu(p));
>
> @@ -1422,14 +1524,21 @@ static enum hrtimer_restart inactive_task_timer(struct hrtimer *timer)
>
> goto unlock;
> }
> +
> +no_task:
> if (dl_se->dl_non_contending == 0)
> goto unlock;
>
> sub_running_bw(dl_se, &rq->dl);
> dl_se->dl_non_contending = 0;
> unlock:
> - task_rq_unlock(rq, p, &rf);
> - put_task_struct(p);
> +
> + if (!dl_server(dl_se)) {
> + task_rq_unlock(rq, p, &rf);
> + put_task_struct(p);
> + } else {
> + rq_unlock(rq, &rf);
> + }
>
> return HRTIMER_NORESTART;
> }
> @@ -1487,34 +1596,35 @@ static void dec_dl_deadline(struct dl_rq *dl_rq, u64 deadline)
> static inline void inc_dl_deadline(struct dl_rq *dl_rq, u64 deadline) {}
> static inline void dec_dl_deadline(struct dl_rq *dl_rq, u64 deadline) {}
>
> +static inline void update_dl_migration(struct dl_rq *dl_rq) {}
> +
> #endif /* CONFIG_SMP */
>
> static inline
> void inc_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
> {
> - int prio = dl_task_of(dl_se)->prio;
> u64 deadline = dl_se->deadline;
>
> - WARN_ON(!dl_prio(prio));
> dl_rq->dl_nr_running++;
> add_nr_running(rq_of_dl_rq(dl_rq), 1);
>
> inc_dl_deadline(dl_rq, deadline);
> - inc_dl_migration(dl_se, dl_rq);
> + if (!dl_server(dl_se))
> + inc_dl_migration(dl_se, dl_rq);
> + update_dl_migration(dl_rq);
> }
>
> static inline
> void dec_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
> {
> - int prio = dl_task_of(dl_se)->prio;
> -
> - WARN_ON(!dl_prio(prio));
> WARN_ON(!dl_rq->dl_nr_running);
> dl_rq->dl_nr_running--;
> sub_nr_running(rq_of_dl_rq(dl_rq), 1);
>
> dec_dl_deadline(dl_rq, dl_se->deadline);
> - dec_dl_migration(dl_se, dl_rq);
> + if (!dl_server(dl_se))
> + dec_dl_migration(dl_se, dl_rq);
> + update_dl_migration(dl_rq);
> }
>
> static inline bool __dl_less(struct rb_node *a, const struct rb_node *b)
> @@ -1676,8 +1786,7 @@ enqueue_dl_entity(struct sched_dl_entity *dl_se, int flags)
> } else if (flags & ENQUEUE_REPLENISH) {
> replenish_dl_entity(dl_se);
> } else if ((flags & ENQUEUE_RESTORE) &&
> - dl_time_before(dl_se->deadline,
> - rq_clock(rq_of_dl_rq(dl_rq_of_se(dl_se))))) {
> + dl_time_before(dl_se->deadline, rq_clock(rq_of_dl_se(dl_se)))) {
> setup_new_dl_entity(dl_se);
> }
>
> @@ -1762,14 +1871,6 @@ static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags)
> enqueue_pushable_dl_task(rq, p);
> }
>
> -static void __dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags)
> -{
> - update_stats_dequeue_dl(&rq->dl, &p->dl, flags);
> - dequeue_dl_entity(&p->dl, flags);
> -
> - if (!p->dl.dl_throttled)
> - dequeue_pushable_dl_task(rq, p);
> -}
>
> static void dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags)
> {
> @@ -1778,7 +1879,9 @@ static void dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags)
> if (p->on_rq == TASK_ON_RQ_MIGRATING)
> flags |= DEQUEUE_MIGRATING;
>
> - __dequeue_task_dl(rq, p, flags);
> + dequeue_dl_entity(&p->dl, flags);
> + if (!p->dl.dl_throttled)
> + dequeue_pushable_dl_task(rq, p);
> }
>
> /*
> @@ -1968,12 +2071,12 @@ static void check_preempt_curr_dl(struct rq *rq, struct task_struct *p,
> }
>
> #ifdef CONFIG_SCHED_HRTICK
> -static void start_hrtick_dl(struct rq *rq, struct task_struct *p)
> +static void start_hrtick_dl(struct rq *rq, struct sched_dl_entity *dl_se)
> {
> - hrtick_start(rq, p->dl.runtime);
> + hrtick_start(rq, dl_se->runtime);
> }
> #else /* !CONFIG_SCHED_HRTICK */
> -static void start_hrtick_dl(struct rq *rq, struct task_struct *p)
> +static void start_hrtick_dl(struct rq *rq, struct sched_dl_entity *dl_se)
> {
> }
> #endif
> @@ -1993,9 +2096,6 @@ static void set_next_task_dl(struct rq *rq, struct task_struct *p, bool first)
> if (!first)
> return;
>
> - if (hrtick_enabled_dl(rq))
> - start_hrtick_dl(rq, p);
> -
> if (rq->curr->sched_class != &dl_sched_class)
> update_dl_rq_load_avg(rq_clock_pelt(rq), rq, 0);
>
> @@ -2018,12 +2118,26 @@ static struct task_struct *pick_task_dl(struct rq *rq)
> struct dl_rq *dl_rq = &rq->dl;
> struct task_struct *p;
>
> +again:
> if (!sched_dl_runnable(rq))
> return NULL;
>
> dl_se = pick_next_dl_entity(dl_rq);
> WARN_ON_ONCE(!dl_se);
> - p = dl_task_of(dl_se);
> +
> +
> + if (dl_server(dl_se)) {
> + p = dl_se->server_pick(dl_se);
> + if (!p) {
> + // XXX should not happen, warn?!
> + dl_se->dl_yielded = 1;
> + update_curr_dl_se(rq, dl_se, 0);
> + goto again;
> + }
> + p->server = dl_se;
> + } else {
> + p = dl_task_of(dl_se);
> + }
>
> return p;
> }
> @@ -2033,9 +2147,20 @@ static struct task_struct *pick_next_task_dl(struct rq *rq)
> struct task_struct *p;
>
> p = pick_task_dl(rq);
> - if (p)
> + if (!p)
> + return p;
> +
> + /*
> + * XXX: re-check !dl_server, changed from v2 because of
> + * pick_next_task_dl change
> + */
> + if (!dl_server(&p->dl))
> set_next_task_dl(rq, p, true);
>
> + /* XXX not quite right */
> + if (hrtick_enabled(rq))
> + start_hrtick_dl(rq, &p->dl);
> +
> return p;
> }
>
> @@ -2073,8 +2198,8 @@ static void task_tick_dl(struct rq *rq, struct task_struct *p, int queued)
> * be set and schedule() will start a new hrtick for the next task.
> */
> if (hrtick_enabled_dl(rq) && queued && p->dl.runtime > 0 &&
> - is_leftmost(p, &rq->dl))
> - start_hrtick_dl(rq, p);
> + is_leftmost(&p->dl, &rq->dl))
> + start_hrtick_dl(rq, &p->dl);
> }
>
> static void task_fork_dl(struct task_struct *p)
> @@ -3003,6 +3128,7 @@ static void __dl_clear_params(struct sched_dl_entity *dl_se)
> dl_se->dl_yielded = 0;
> dl_se->dl_non_contending = 0;
> dl_se->dl_overrun = 0;
> + dl_se->dl_server = 0;
>
> #ifdef CONFIG_RT_MUTEXES
> dl_se->pi_se = dl_se;
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index fda67f05190d..0c58d8e55b69 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -930,6 +930,8 @@ s64 update_curr_common(struct rq *rq)
>
> account_group_exec_runtime(curr, delta_exec);
> cgroup_account_cputime(curr, delta_exec);
> + if (curr->server)
> + dl_server_update(curr->server, delta_exec);
>
> return delta_exec;
> }
> @@ -958,6 +960,8 @@ static void update_curr(struct cfs_rq *cfs_rq)
> trace_sched_stat_runtime(curtask, delta_exec, curr->vruntime);
> cgroup_account_cputime(curtask, delta_exec);
> account_group_exec_runtime(curtask, delta_exec);
> + if (curtask->server)
> + dl_server_update(curtask->server, delta_exec);
> }
>
> account_cfs_rq_runtime(cfs_rq, delta_exec);
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index aaf163695c2e..390c99e2f8a8 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -324,6 +324,35 @@ extern bool dl_param_changed(struct task_struct *p, const struct sched_attr *att
> extern int dl_cpuset_cpumask_can_shrink(const struct cpumask *cur, const struct cpumask *trial);
> extern int dl_cpu_busy(int cpu, struct task_struct *p);
>
> +/*
> + * SCHED_DEADLINE supports servers (nested scheduling) with the following
> + * interface:
> + *
> + * dl_se::rq -- runqueue we belong to.
> + *
> + * dl_se::server_has_tasks() -- used on bandwidth enforcement; we 'stop' the
> + * server when it runs out of tasks to run.
> + *
> + * dl_se::server_pick() -- nested pick_next_task(); we yield the period if this
> + * returns NULL.
> + *
> + * dl_server_update() -- called from update_curr_common(), propagates runtime
> + * to the server.
> + *
> + * dl_server_start()
> + * dl_server_stop() -- start/stop the server when it has (no) tasks
> + *
> + * dl_server_init()
> + *
> + * XXX
> + */
> +extern void dl_server_update(struct sched_dl_entity *dl_se, s64 delta_exec);
> +extern void dl_server_start(struct sched_dl_entity *dl_se);
> +extern void dl_server_stop(struct sched_dl_entity *dl_se);
> +extern void dl_server_init(struct sched_dl_entity *dl_se, struct rq *rq,
> + dl_server_has_tasks_f has_tasks,
> + dl_server_pick_f pick);
> +
> #ifdef CONFIG_CGROUP_SCHED
>
> struct cfs_rq;
> --
> 2.40.1
>
--
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